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Thu, 23 Jan 2025 01:49:30 -0800 (PST) MIME-Version: 1.0 References: <20250122152738.1173160-1-tabba@google.com> <20250122152738.1173160-3-tabba@google.com> In-Reply-To: From: Fuad Tabba Date: Thu, 23 Jan 2025 09:48:53 +0000 X-Gm-Features: AWEUYZmCLCgbEEVBEV5FFMaLev25KTqqUcEcZLSpslypZ2rETPMziZWnGfHJ8xk Message-ID: Subject: Re: [RFC PATCH v1 2/9] KVM: guest_memfd: Add guest_memfd support to kvm_(read|/write)_guest_page() To: David Hildenbrand Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6C5852000A X-Stat-Signature: 86eugy3tqu63585gp6shc5mtedwy18fa X-HE-Tag: 1737625771-758886 X-HE-Meta: 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 hyIxU000 OmPqyQcFIrIiQ002KqDZgVDTvUW+7ChlUROSsnyPFyzQTUAaY9a+GsOeXJxEYVk2WabGakuBx4Gc3dxPDxKFxnV7TbpPZUcQIOqQnOGIUrA/O/2sljOHLjckWcSgldr01VO6phmqscUw+Kp3vBgDlp8nu5IS4EQePDysBpk2VhVk+irlOCiJX1xTTL0PlRnUPI6QTHdVWIY3ECbigeJrCvcc7S4InobR7SNhgGb11B4Ncz5CFVlrIkOgSrIAdRvoqah8mr/jHsevUSBYB/v8LhiSro4dMBCh7Ru/1BjrOUdCfPG76PCGZn2+qxzTMQzYYTU6U/PCatRYgn/xqSxQE9NwRDwyNqlEhcan48sjPHbs6mIfZp3ADdQKpZpZzWT1SM84T X-Bogosity: Ham, tests=bogofilter, spamicity=0.031883, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 22 Jan 2025 at 22:10, David Hildenbrand wrote: > > On 22.01.25 16:27, Fuad Tabba wrote: > > Make kvm_(read|/write)_guest_page() capable of accessing guest > > memory for slots that don't have a userspace address, but only if > > the memory is mappable, which also indicates that it is > > accessible by the host. > > Interesting. So far my assumption was that, for shared memory, user > space would simply mmap() guest_memdd and pass it as userspace address > to the same memslot that has this guest_memfd for private memory. > > Wouldn't that be easier in the first shot? (IOW, not require this patch > with the cost of faulting the shared page into the page table on access) This has to do more with the ABI I had for pkvm and shared memory implementations, in which you don't need to specify the userspace address for memory in a guestmem memslot. The issue is there is no obvious address to map it to. This would be the case in kvm:arm64 for tracking paravirtualized time, which the userspace doesn't necessarily need to interact with, but kvm does. That said, we could always have a userspace address dedicated to mapping shared locations, and use that address when the necessity arises. Or we could always require that memslots have a userspace address, even if not used. I don't really have a strong preference. Thanks, /fuad > -- > Cheers, > > David / dhildenb >